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I did not have the AC on. What temperature does the fans come on? Where should my temp gauge be when the fans kick in?
When you press the AC button, the two front fans come on at low speed and stay on at low speed. This is almost a required action for our car’s to stay cool, and I believe it even states that this is the preferred operation in the manual.
”Engine Thermostat
The OEM thermostat starts to open at 187 degrees and is fully open at 210 degrees.
Between the 8 and 0 is 194F, Right in the middle of 0 is 100C. Right edge of 0 is 103-105C.
Bruce Anderson's air-cooled temp chart (still applies to liquid cooled cars to some degree, because oil temp is related to overall temp, and oil can be responsible for nearly 1/2 of all cooling of an engine):
180-220 is normal
230 is warm
240 is hot
250 is too damn hot
Electric fans
There are two radiator modules installed in the front of the vehicle (on the left- and right-hand side). These radiators are each fitted with an electric fan. They can be operated at two speeds and are activated by the DME control unit whenever the following conditions apply:
Electric fan, speed 1
(Ground to DME control unit, terminal 35)
Coolant temperature higher than 96.75°C or air conditioning switched on.
Electric fan, speed 2
(Ground to DME control unit, terminal 36)
Coolant temperature > 102°C or air-conditioning fluid pressure switch closed (coolant pressure > 16 bar).
Note: The electric fans for the radiators are only triggered when the engine is running!
Engine bay fan:
The engine compartment purge fan rarely comes on. This fan will not really cool the engine, but instead, keep the engine bay from getting too hot.
From the service manual...
"Switch-on conditions for engine compartment fan (this fan pulls air into the engine compartment) The engine compartment fan is switched on when the engine compartment temperature is > 176 degrees F or the coolant temperature is > 216 degrees F.
After-running of engine compartment fan
If the ignition is switched off and the engine compartment temperature is more than 140 degrees F, the DME control module remains in readiness for another 20 minutes. During this time, the engine compartment temperature is retrieved every 10 seconds. If the engine compartment temperature is > 185 degrees F , the engine compartment fan is switched on for 20 seconds. If the engine compartment temperature is still > 185 degrees F after this time, the fan remains on for a further 30 seconds."
Here is the long explanation from the service manual on the flashing coolant light (on the dash):
"Four functions of the coolant warning light:
1. Engine coolant level too low -- light flashes slowly (0.5 Hz)
2. Engine compartment temperature too high -- light flashes slowly (0.5 Hz) (engine compartment blower might be faulty)
3. Engine coolant temperature too high -- light is lit; pointer on the right
4. Temperature sensor at water outlet faulty -- light flashes rapidly (1 Hz) ; pointer on the right
Note: The temperature warning in point three is indicated if the conditions "engine coolant temperature too high" and "engine coolant level too low" are present simultaneously."
Yesterday i went on skne backroads driving, and after stopping, my friends always leave their BMWs on to cool down. Is this a good practice to leave the car on for a few minutes to cool down? How long would i leave it on?
Yesterday i went on skne backroads driving, and after stopping, my friends always leave their BMWs on to cool down. Is this a good practice to leave the car on for a few minutes to cool down? How long would i leave it on?
I have a C2 3.4.
It depends.
It makes sense to cool things down for a few mins after a hard run by slowing down to normal speed and allowing air to move through the brakes and heat exchangers (radiators, oil coolers, trans coolers, etc. This is best accomplished on the cool down lap after tracking the car, and if the engine and brakes are hot, you can watch the gauge actually drop a bit.
If you have no time to do this, then the car should idle for a few mins, with the AC button on, but then should not idle any longer. Idling for more than a few mins actually doesn’t cool the engine down at all, unless the car is equipped with post-shutdown active cooling (such as the Dodge Demon). Our car’s don’t have active cooling aside from the engine bay fan, but that fan doesn’t actually cool the engine itself.
Yesterday i went on skne backroads driving, and after stopping, my friends always leave their BMWs on to cool down. Is this a good practice to leave the car on for a few minutes to cool down? How long would i leave it on?
I have a C2 3.4.
Do your friends happen to have turbo BMWs? My guess is that they are leaving their engines running to help cool the turbos before shutting them off. The e90 335i has expensive turbos and there may be some value letting the engine run for a few minutes after a particularly hard workout. Although the n54 engine does use an electric coolant pump and will run the coolant through the turbos after the engine is shut off, so the value in letting the car idle is debatable.
It makes sense to cool things down for a few mins after a hard run by slowing down to normal speed and allowing air to move through the brakes and heat exchangers (radiators, oil coolers, trans coolers, etc. This is best accomplished on the cool down lap after tracking the car, and if the engine and brakes are hot, you can watch the gauge actually drop a bit.
If you have no time to do this, then the car should idle for a few mins, with the AC button on, but then should not idle any longer. Idling for more than a few mins actually doesn’t cool the engine down at all, unless the car is equipped with post-shutdown active cooling (such as the Dodge Demon). Our car’s don’t have active cooling aside from the engine bay fan, but that fan doesn’t actually cool the engine itself.
+!, nothing cools my 996 like cruising above 40mph. Stop & go or waiting around in idle keep temps elevated.
Do your friends happen to have turbo BMWs? My guess is that they are leaving their engines running to help cool the turbos before shutting them off. The e90 335i has expensive turbos and there may be some value letting the engine run for a few minutes after a particularly hard workout. Although the n54 engine does use an electric coolant pump and will run the coolant through the turbos after the engine is shut off, so the value in letting the car idle is debatable.
Excellent information in this tread again. Yes, one friend has a 2018 M3, and the other has a 500+ hp 335i, single turbo conversion very much built. When we stop, I have my car off, and they have their cars cooling down. Good to know that I am not doing anything majorly bad to my car. Although my car had the least hp, mine was the most fun driving through the twisties. This was my first time really hitting the twisties hard, and going on a group drive.
Year 2000 had these issues. Shortly after Porsche put in switch rather than rheostat to show engine temp either Cold, Warm or Hot. No in between. Both of my 2000 996 have done this. Complete cooling system and third radiator ALL replaced. No change. Save your money!!!! It's normal! But as another lister posted picture of water pump impellers could be culprit...
Excellent information in this tread again. Yes, one friend has a 2018 M3, and the other has a 500+ hp 335i, single turbo conversion very much built. When we stop, I have my car off, and they have their cars cooling down. Good to know that I am not doing anything majorly bad to my car. Although my car had the least hp, mine was the most fun driving through the twisties. This was my first time really hitting the twisties hard, and going on a group drive.
If anything, those BMW folks aren’t doing their engines any favors. I have a BMW friend that like to start his M46 in the cold and let it idle for 20 mins to warm up. Not the best idea. That same guy let his engine idle for 15 mins after leaving the track. Also not good. Then, he waits until the last minute to start his car before heading out to the track - not good either, as he starts whomping on it before it fully gets up to temp.
It must be a BMW thing, lol.
Glad to hear the 996 was the most fun. I’d agree with that when compared to a new M3 or a 335, but when compared to an older M3 or the 135, it might be a closer comparison.
Year 2000 had these issues. Shortly after Porsche put in switch rather than rheostat to show engine temp either Cold, Warm or Hot. No in between. Both of my 2000 996 have done this. Complete cooling system and third radiator ALL replaced. No change. Save your money!!!! It's normal! But as another lister posted picture of water pump impellers could be culprit...
I have a 2000 C2. In temps above 80ish it runs at or a little above the third white line (Not Red Line). I had a coolant flush and had the radiators cleaned (bumper off). Didn't change the running temp. I used the Durametric tool to evaluate the actual running temperature. Turns out it was running in the low to mid 220s depending on whether I was driving or sitting in traffic. Turns out, from what my indy said, that there isn't an issue...hmmmm
Newer 996 owner here. After a 30 minute commute: stop and go traffic warm up, 15 miles sustained 80-105 cruising, stop and go and then park. Temps between 212-224 and all fans running, including engine fan after-run. 75-80 degree ambient temp and the temp needle is pointing to the 0 in 180.
I'm going to clean the radiators and replace the WP and t-stat for good measure, however it seems to be the normal operating temp for these cars. HOT.
It makes sense to cool things down for a few mins after a hard run by slowing down to normal speed and allowing air to move through the brakes and heat exchangers (radiators, oil coolers, trans coolers, etc. This is best accomplished on the cool down lap after tracking the car, and if the engine and brakes are hot, you can watch the gauge actually drop a bit.
If you have no time to do this, then the car should idle for a few mins, with the AC button on, but then should not idle any longer. Idling for more than a few mins actually doesn’t cool the engine down at all, unless the car is equipped with post-shutdown active cooling (such as the Dodge Demon). Our car’s don’t have active cooling aside from the engine bay fan, but that fan doesn’t actually cool the engine itself.
The best thing to do to cool things down is driving on the highway at easy steady speed, so low load on the engine and enough air going through the rads, and then keeping it revved higher around 3500-4000rpm.
This makes the water pump spin fast and to pump a lot of coolant through the block. When doing so I see oil temperatures drop considerably fast as more and cooler coolant also flows through the oil/water heat exchanger.
Idling after a hard drive is not so effective as the easy high rev cooling off drive. The coolant needs the air flowing trough the roads to cool. No fan can compensate for driving wind. Idling only makes the coolant and block heat up more, till the fans go on.
My coolant is steady at 80-90 degC independent the driving conditions and ambient temperatures (Oil is 90-110 degC). Coolant reaches the higher eighties only when in stop and go traffic, or idling, guess what, when there is not enough driving wind. My fans are reprogrammed to kick in at a lower temperature and get their value from another sensor at a better location.
My car is a 2002 996 C2 with Relocated LTT, GT3 waterpump
So,leaving the ac button on is actually better for cooling the temps? I have a new water pump, low stat and new coolant and I'm still running around what others have posted in their pictures...
So,leaving the ac button on is actually better for cooling the temps? I have a new water pump, low stat and new coolant and I'm still running around what others have posted in their pictures...
In city stop and go driving...yes. Having the AC on triggers the low speed fans on automatically. With the AC off, the fans only come on based on the engine temperature. At speeds above 40-45 MPH, probably not as important because there is enough air flow through the radiators to keep things cool.
So,leaving the ac button on is actually better for cooling the temps? I have a new water pump, low stat and new coolant and I'm still running around what others have posted in their pictures...
Yes, Its basically all I do. Without it, 107C easily. With AC on, I’m 3-6C cooler. Try it and report back. Note: I don’t wait until my temps are high, because it can take a long time to start cooling down. I turn on the AC before the car gets hot.
03-31-2018, 12:52 PM
